The present invention relates to a detector device for combustion state in an internal combustion engine, and, more particularly, to a detector device for combustion state in an internal combustion engine which enables it to detect misfire over the entire operating range where the internal combustion engine generates positive torque.
Conventionally, technique has been known that indirectly detects misfire by measuring the engine speed utilizing the relationship between torque generated by combustion of an engine and the engine speed in order to detect operating condition. Examples of such technique include Japanese Patent Unexamined Publication No. 58-51243. This technique is to detect the engine speed at least two points in one ignition cycle from the previous ignition to the current ignition, to determine a variation in the engine speed in the one ignition cycle from the difference of the engine speed, to statistically process the sequentially determined variations in the engine speed, and to determine the combustion state of the internal combustion engine by using the result of process.
The approach for determining the combustion state of the internal combustion engine by detecting the engine speed is performed by detecting a rotation angle of a ring gear or plate mounted on a crank shaft. However, experiments by the inventors revealed that, although the approach was effective in a relatively low rotation range, it suffered from difficulty in properly judging the combustion state in the internal combustion engine in a high rotation range because dispersion in error in manufacturing pitch of the ring gear or plate became significant in the high rotation range, and influence of such pitch error became high.